Method for determining a characteristic value for the binding force potential of suspended paper fibers and use of this method

ABSTRACT

The method is used for determining a characteristic value for the binding force potential of paper fibers present in a fibrous suspension prepared for paper manufacture. According to the invention, the air content of the fibrous suspension is measured and this characteristic value derived therefrom. The correlation between the characteristic value and the air content ascertained can be discovered, e.g. by means of series of empirical measurements. With the aid of this method, e.g., the runnability on the paper machine can be assessed and corrected before breakdowns occur.

[0001] The invention relates to a method according to the preamble of claim 1.

[0002] In paper manufacture it is known that paper fibers are placed in an aqueous fibrous suspension on the paper machine and dewatered. The paper fibers touching each other thereby develop binding forces which ultimately lead to the formation of a firmly cohesive sheet of paper. The possibility of developing such binding forces, i.e., the binding force potential, depends on a plurality of parameters. The most important are fiber condition and fiber size, as well as the chemical and material environment in the suspension. Improving the binding force potential is often associated with costs for raw material quality, processing and the use of chemical aids. It is therefore desirable to be able to determine the binding force potential in a timely manner, i.e., before the actual paper production, so as to be able to optimize the entire process.

[0003] The object of the invention is therefore to create a method with which the binding force potential of paper fibers in an aqueous suspension can be characterized. In particular, it should render possible the detection of deviations from the desired binding force potential in a timely manner. The measurement is to lead to quick measurement readings.

[0004] This object is attained by means of the features specified in the characterizing part of claim 1.

[0005] Particularly useful measuring data are obtained at the point where no measures have yet been taken for the effective deaeration of the fibrous suspension. Here the air content can freely adjust according to the fiber technology and chemical parameters of the fiber stock prepared for paper manufacture. Surprisingly, the correlation of the air content measured at this point and the binding force potential can be defined with sufficient accuracy that an early prediction can be made of certain paper properties to be expected. This correlation can be easily determined, e.g., by means of empirical measurements even without all causalities being known. It can be assumed that the air content itself is not important for binding force potential, but it serves merely as an indicator. In many cases a higher binding force potential was established with a higher air content.

[0006] In practice the air content measurement is made, e.g., in the approach flow system of the paper mill after the mixing pump in which the paper stock is mixed with the diluting water and brought to the required stock consistency. If the paper or cardboard is to be produced from different sorts, the characteristic values for these sorts can also be separately determined and corrections made individually.

[0007] Various possibilities are conceivable for reacting to the deviation of the characteristic value from its set value: the use of chemical agents, changing the fiber treatment or composition or adjusting the paper machine up to reducing the wire speed.

[0008] With the aid of the method according to the invention, the paper machine process can be brought up to optimum runnability on the paper machine simply and economically. It makes it possible to correct the binding force potential in a timely manner, i.e., before a break has occurred on the paper machine. It is known that the prevention of breaks is a very important economic advantage in paper manufacture.

[0009] The invention and its advantages will be explained by means of a drawing.

[0010] According to this drawing, the already prepared fiber stock 1 is mixed with the diluting water 2, which originates from, e.g., the back water of the paper machine, in the mixing pump 3. A fibrous suspension is thus formed which has the stock consistency which is provided for the operation of the paper machine. In the example shown here, this fibrous suspension first arrives via a feedpipe 5 at a cleaner battery 8 and then at a deaeration container 9. The feedpipe 5 brings the fibrous suspension to a higher geodetical level, which facilitates deaeration by vacuum. It is known that the cleaner battery 8 is used for the precipitation of fine heavy parts, and the deaeration container 9 for removing the air 10 from the suspension with the aid of vacuum. Such and similar treatment steps are known per se, and so just this one possibility is shown diagrammatically. In connection with the method according to the invention, it is advantageous if the measuring point 4, at which the air content measurement is made, is located where the deaeration of the fibrous suspension has not yet been carried out. From measuring point 4 a regulator 7 is controlled via a signal line 6, which regulator can trigger the corrections or control actions described above. As shown here by way of example, this can be the control of a proportioning pump 14 with which a chemical retention agent 15 is added to the suspension. Alternatively, this figure shows two other measuring points at which the as yet undiluted fiber stock 1 is measured, e.g., in the drain pipe of the corresponding vat 13 (measuring point 4′) or with a stock sample taken from the vat 13 (measuring point 4″).

[0011] The cleaned and deaerated fibrous suspension is guided through an outlet pipe 11 to the pump 12 from which it can reach, e.g., the proportioning system or the headbox of a paper machine. The proportioning system is used e.g. for mixing different components used in paper manufacture. 

1. Method for determining a characteristic value for the binding force potential of paper fibers in a fibrous suspension prepared for paper manufacture, characterized in that the air content of the fibrous suspension is measured and that the characteristic value is derived therefrom.
 2. Method according to claim 1, characterized in that the air content is measured at a measuring point (4, 4′, 4″) in the fiber stock preparation process at which the fibrous suspension has the stock composition necessary for paper manufacture, without the air content having been adjusted by a corresponding deaeration process.
 3. Method according to claim 2, characterized in that the air content is measured in the approach flow system of a paper mill after the mixing pump (3) in which the fiber stock (1) is mixed with diluting water (2).
 4. Method according to claim 2, characterized in that the air content in the approach flow system of a paper mill is measured before the mixing pump (3) in which the fiber stock (1) is mixed with diluting water.
 5. Method according to claim 2, 3 or 4, characterized in that after measuring the air content, the fibrous suspension is deaerated by means of a vacuum.
 6. Method according to one of the above claims, characterized in that several sorts of fiber stock are used for paper manufacture at the same time, and that the air content is measured separately in the sorts.
 7. Method according to one of the above claims, characterized in that the characteristic value for the binding force potential is assigned to the air content with the aid of corresponding empirical values.
 8. Method according to claim 7, characterized in that the empirical values are determined by measuring the strengths of the sheets formed from the suspension.
 9. Method according to claim 7, characterized in that the empirical values are assigned to the paper machine by determining the runnability achieved with the fibrous suspension.
 10. Use of the method according to one of the above claims, characterized in that the amount of strengthening chemicals and/or retention agents added to the fibrous suspension is adjusted such that a characteristic value which was stipulated as useful is maintained.
 11. Use of the method according to one of the above claims, characterized in that the amount of strengthening chemicals and/or retention agents added to the fibrous suspension is minimized according to the demands on runnability. 